This invention relates to an improved process for the preparation of urethanes in which urea or polyurets, amines and alcohols are reacted in the presence of N-unsubstituted urethanes and/or N-mono- or N,N'-disubstituted ureas or polyureas.
It is known that urethanes may be formed by reacting organic isocyanates with alcohols. This reaction is reversible, i.e., the urethanes so formed may be thermally split into the isocyanate and the alcohol on which they are based (see, for example, U.S. Pat. No. 2,409,712). Urethanes which may be thermally split into isocyanates are, therefore, potential starting materials for the preparation of isocyanates.
Isocyanates have been almost universally prepared by reacting primary amines with phosgene. However, the preparation of urethanes without phosgene and the subsequent thermal splitting of these urethanes would be an interesting alternative. One method for preparing urethanes without the use of phosgene is to react urea with amines and alcohol. Such a method is described in U.S. Pat. Nos. 2,409,712 and 2,806,051. However, these known methods produce urethanes which contain numerous secondary products in inadequate yields.